ALBERT

Notes: The kinetics of N-phenylphthalamic acid and of N-phenylphthalimide hydrolysis in aqueous solutions of sulfuric acid has been studied. A reaction mechanism is proposed implying that unreactive forms of the reactant appear by protonization of the amide bond at the carbonyl oxygen and by dissociation of the o-carboxyl group (N-phenylphthalamic acid). Attack of the nonprotonized amide bond by the hydroxonium ion is suggested to be the rate-limiting step.

Notes: Electronically excited oxygen atoms O(21D2) have been generated by the pulsed irradiation of ozone in the Hartley-band continuum and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation at λ = 115.2 nm [O(31D2°) → O(21D2)]. Collisional quenching of the excited atom has been investigated for all the noble gases, and the first absolute values for the second-order deactivation rate constants are reported. The resulting rate data are discussed in terms of a curve-crossing mechanism based on existing spectroscopic data for the noble gas oxides. The absolute rate constants are compared with previous relative rate data for the deactivation of O(21D2) by the noble gases.

Notes: The rate constant for the reaction I(2P1/2) + CH3I → I2 + CH3 has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I2 by I2 + CH3 → I + CH3I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys., 46, 4146 (1967) from the flash photolysis of CH3I using time-resolved mass spectrometry to measure the rate of I2 formation. Computer simulations of the complete kinetic system and a closed-form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 106 1./mole-sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I(2P1/2) with CH3I was also determined (2.4 × 107 1./mole-sec).

Notes: Competitive studies of the reactions of ground-state oxygen atoms, generated by mercury-photosensitized decomposition of nitrous oxide, have been carried out with ethylene and all the fluoroethylenes using 2-(trifluoromethyl)-propene as reference compound. From measurements at 25°C and 150°C relative rate constants have been determined and used to calculate the Arrhenius parameters shown in the following table: TextOlefin\documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{A_{{\rm olefin}} }}{{A_{{\rm 2TFMP}} }}$$\end{document}ΔERef\documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{A_{{\rm olefin}} }}{{A_{{\rm C}_{\rm 2} {\rm H}_{\rm 4} } }}$$\end{document}ΔEC2H4CH2—CH21.10-1.18(1.0)(0)CH2—CHF1.030.840.942.02CH2—CF20.711.490.652.67CHF—CHF (cis-)1.231.921.123.10CHF—CHF (trans-)1.400.791.271.97CF2—CHF1.060.000.961.22CF2—CF20.86-3.220.78-2.04ΔERef = Eolefin - E2TFMP and ΔEC2H4 = Eolefin - EC2H4. Units are kJ/mole.The results are compared with corresponding data for other atoms and radicals, and discussed in terms of the electronic changes produced in the double bond by fluorine substitution, and in relation to the nature of the transition state.

Notes: Nucleophilic substitution reactions in the alkyl halides, RX + Y- → RY + X-, proceeding in polar media are considered on the basis of the theory presented in Part A. It is shown that the solvent reorganization energy is the main part of the activation energy for this processes. According to calculations performed, the values of the solvent reorganization energy equal ∼2.5-3 eV for H2O and ∼ 1.8-2.3 eV for acetone. From experimental data on the kinetic isotope effect, an estimate for the splitting of nonadiabatic terms and for the slope of the potential curve v′ of the intermolecular interaction between halide ion and methyl halide near transition configuration is made. Further, the parameter v′ is used for calculating the activation entropy of substitution reactions in the methyl halides. Theoretical activation energies and activation entropies agree with experimental values. In the framework of theory presented an interpretation of change of Ea and the preexponential factor with the type of alkyl halide is given.

Notes: The kinetics of the thermal decomposition of diallylamine to propylene and prop-2-enaldimine have been studied in the gas phase in presence of an excess of methylamine over the temperature range of 532.7 to 615.6°K, using a static reaction system. Methylamine reacted with the unstable primary product prop-2-enaldimine, forming the thermally stable N-methyl prop-2-enaldimine.First-order rate constants, based on the internal standard technique, fit the Arrhenius relationship log k(s-1) = (11.04 ± 0.13) - (37.11 ± 0.33 kcal/mole)/2.303 RT. They were independent on the initial total pressure (46-340 torr), the initial pressure of diallylamine (9.2-65 torr), or methylamine as well as the conversion attained. Despite an apparent surface sensitivity, the reaction is essentially homogeneous in nature as demonstrated by experiments carried out in a packed reaction vessel.The observed activation parameters for the title reaction together with those observed earlier for triallylamine and allylcyclohexylamine are consistent with the proposed concerted reaction mechanism involving a cyclic 6-center transition state. The observed substituent effects suggest a nonsynchronous mode of bond breaking and bond formation.

Notes: Activation energies for substitution reactions of the type AC + B → A + CB, occurring in polar media and characterized by an abrupt change of the term along two coordinates have been calculated within the framework of the quantum-mechanical theory of chemical reactions. In the case of nonadiabatic processes, the transmission coefficient and activation energy for these reactions are expressed in terms of characteristic parameters of the medium (reorganization energy, effective frequency of solvent fluctuation polarization) and the potential energy curves for intermolecular interactions between the reactants (AC and B) and between the products (A and BC).

Notes: The thermal decomposition of ethylallylether (EAE) has been studied in the gas phase over the temperature range of 560-648°K. Propylene and acetaldehyde are the only reaction products observed. The reaction is apparently homogeneous in nature and independent of the pressure of EAE and of added foreign gases. The experimetally determined first-order rate constants, using the internal standard technique, fit the Arrhenius relationship log k(s-1) = 11.84 ± 0.29 - (43.57 ± 0.77 kcal/mole)/2.303RT. Independently the same rate constants are obtained, based on the amounts of products formed. The observed activation parameters are in general agreement with expectations based on the concept of a 6-center 1,5-H-shift retro-“ene” reaction mechanism, and they agree with previous results obtained for the similar reactions involving alkylallylamines and olefins.

Notes: A competitive method involving the direct measurement of radical concentrations by EPR spectroscopy has been used to show that in solution at 25°C the rate constants for the bimolecular self-reactions of ethyl, isopropyl, tert-butyl, cyclopentyl, and trichloromethyl are all approximately equal, as had been indicated previously by direct measurement of the rate constants for decay of these radicals.

Notes: Predictions of the “redox” and “complex” schemes for the Fe3+ catalyzed decomposition of H2O2 have been compared with published and new experimental data by numerical integratior of the appropriate complete sets of differential equations. Apparent discrepancies for the redox scheme at high Fe3+/H2O2 ratios are shown to disappear in the complete treatment, and inconsistencies of the complex scheme with both kinetic data and spectroscopic measurements are pointed out.

Notes: The effect of reactant self-heating or cooling upon rate data is considered, and three approaches to the problem of obtaining valid kinetic parameters are described in detail. A comparison of these approaches emphasises the need to assess and allow for thermal effects during the initial planning of kinetic experiments if satisfactory results are to be acquired. An integrated rate expression is given for use with nonisothermal data, and is used to provide correction factors for rate constants which have been derived without allowance for thermal effects.

Notes: The reaction of O(3P), prepared from the Hg photosensitization of N2O, with C2HCl3 was studied at 25°C. The products of the reaction in the absence of O2 were CO, CHCl3, and polymer (as well as N2 from the N2O). The quantum yields of CO and CHCl3 were 0.23 ± 0.01 and 0.14 ± 0.05, is respectively independent of reaction conditions. The reaction mechanism is with k14a/k14 = 0.23, where k14a + k14b. Most of the HCl and CCl2 combine to form CHCl3, but some other products must also be formed to account for the difference in the CO and CHCl3 quantum yields. The C2HCl3O* adduct polymerizes without involving additional C2HCl3 molecules, since the quantum yield of C2HCl3 disappearance, —Φ{C2HCl3}, was about 1.0 at high values of [N2O]/[C2HCl3]. The rate coefficient for the reaction of O(3P) with C2HCl3 is 0.10 that for the reaction of O(3P) with C2F4.In the presence of O2 the free radical chain oxidation occurs because of the reaction The main product is CHCl2CCl(O) with smaller amounts of CO and CCl2O, and some CO2. The chain lengths were long and values of — Φ {C2HCl3} up to 90 were observed.

Notes: The kinetics of the decay of hydroxyl radicals in the presence of excess acetylene were studied at pressures in the vicinity of 1 torr and at ambient temperature in a tubular discharge-flow reactor. Hydroxyl radicals were produced by the reaction of atomic hydrogen with nitrogen dioxide, H + NO2 → OH + NO. The concentration of hydroxyl was followed by line absorption photometry at 308.939 nm and 308.328 nm. Second-order rate coeffcients were determined in two sets of experiments. The initial concentration ratio [C2H2]0/[OH]0 was in the range of 2.3 to 13.2 in the first set, and 14 to 125 (owing to greater hydroxyl detection sensitivity) in the second set. Values of the second-order rate coefficient obtained were nk5 = (2.9 ± 0.3) × 10-13 cm3/molec-sec in the first set, and nk5 = (2.1 ± 0.6) × 10-13 cm3/molec-sec in the second set, where n is the stoichiometric coefficient of OH. A value of the bimolecular rate constant k5 = (2.0 ± 0.6) × 10-13 cm/molec-sec is consistent with both sets of data, as well as an earlier determination.

Notes: The thermal decomposition of t-butylmethyl ether has been studied using the VLPP technique. The recommended Arrhenius parameters for the molecular elimination, reaction (1), are A(800°K) = 101 3, 9 sec-1 and Ea (800°K) = 59.0 ± 1.0 kcal/mole. No radical reactions occur under the conditions used. These parameters are in good agreement with earlier experimental work and with theoretical estimates of both A and E.

Notes: The chemical reactions of SO2(3B1) molecules with cis- and trans-2-butene have been studied in gaseous mixtures at 25°C by excitation of SO2 within the SO2(3B1) → SO2(+, 1A1) ‘forbidden’ band using 3500-4100-Å light. The initial quatum yields of olefin isomerization were determined as a function of the [SO2]/[2-butene] ratio and added gases, He and O2. The kinetic treatment of these data suggests that there is formed in the SO2(3B1) quenching step with either cis- or trans-2-butene, some common intermediate, probably a triplet addition complex between SO- and olefin. It decomposes very rapidly to form the 2-butene isomers in the ratio [trans-2-butene]/[cis-2-butene] = 1.8. In another series of experiments SO2 was excited using a 3630 ± 1-Å laser pulse of short duration, and the SO2(3B1) quenching rate constants with the 2-butenes were determined from the SO2(3B1) lifetime measurements. The rate constants at 21°C are (1.29 ± 0.18) × 1011 and (1.22 ± 0.15) × 1011 l/mole·sec with cis-2-butene and trans-2-butene, respectively, as the quencher molecule. Within the experimental error these quenching constants equal those derived from the quantum yield data. Thus the rate-determining step in the isomerization reaction is suggested to be the quenching reaction, presumably the formation of the triplet SO2-2-butene addition complex. In a third series of experiments using light scattering measurements, it was found that the aerosol formation probably originates largely from SO3 and H2SO4 mist formed following the reaction SO2(3B1) + SO2 → SO3 + SO(3Σ-). Aerosol formation from photochemically excited SO2-olefin interaction is probably unimportant in these systems and must be unimportant in the atmosphere.

Notes: The decaying absorption of CH3 radicals at 216.4 nm has been followed over more than three half-lives using a photoelectric split-beam kinetic spectrometer. The rate constant for recombination kr was found to be (5.60 ± 0.76) × 10-11 cm3/molecule·s.

Notes: Singlet methylene was reacted with cyclopentadiene to give chemically activated bicyclo[3.1.0]hex-2-ene (BCH). The rate of isomerization of BCH to 1,4-cyclohexadiene, 1,3-cyclohexadiene, cis-1,3,5-hexatriene, and l-methylcyclopentadiene is compared with calculated rate constants using the RRKM theory and measured or estimated thermal Arrhenius parameters. Subsequent isomerizations of the C6H8 products are also measured and calculated. These include 1,4-cyclohexadiene to benzene and the reversible reactions between 1,3-cyclohexadiene, cis-1,3,5-hexatriene, and trans-1,3,5-hexatriene. The results provide new data for several of these reactions which have not been observed in thermal studies. Agreement between the observed and calculated rates using the strong collision assumption is satisfactory except for the trans-1,3,5-hexatriene to cis-1,3,5-hexatriene reaction.

Notes: Study of the reaction by very-low-pressure pyrolysis (VLPP) in the temperature range of 550-850°K yields for the high-pressure Arrhenius parameters \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }\,k_{\rm 1} = (15.6 \pm 0.5) - (36.0 \pm 1.0)/\theta {\rm \,(sec}^{{\rm - 1}})$$\end{document} where θ = 2.303RT in kcal/mole. These in turn yield for the high-pressure second-order recombination of tBu + NO, k-1 = (3.5 ± 1.7) × 109 1./mole·sec at 600°K. For the competing reaction l./mole·sec and E4 ≥ 4.2 kcal/mole. The bond dissociation energy DHo (tBu-NO) was determined to be (39.5 ± 1.5) kcal/mole, both from the equilibrium constant and from the activation energy of reaction (1), obtained from RRKM calculations. A ‘free-volume’ model for the transition state for dissociation is consistent with the data. A limited study of the system at 8-200 torr showed an extremely rapid inhibition by products and a very complex set of products.

Notes: The thermal isomerization of 1,1-divinylcyclopropane has been investigated in the gas phase in the temperature range of 238 to 288°C and for pressures in the range of 4 to 12 torr. The isomerization to 1-vinylcyclopentene is homogeneous and kinetically first order and almost certainly unimolecular. The rate constants yield the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k({\rm s}^{ - 1} {\rm)} = 13.53 \pm 0.13 - (42.45 \pm 0.33{\rm \,kcal/mole})/RT\,{\rm In 10}$$\end{document} or \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k({\rm s}^{ - 1} {\rm)} = 13.53 \pm 0.13 - (117.6 \pm 1.4{\rm \,kJ/mole})/RT\,{\rm In 10}$$\end{document} The assumption of a similar transition state for this isomerization with that of l-methyl-l-vinylcyclopropane leads to a value for an alkylpentadienyl radical stabilisation energy of 19.2 ± 1.6 kcal/mole (80.4 ± 6.7 kJ/mole), and this value is compared with other estimates.

Notes: Vinylacetylene was pyrolyzed at 300-450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half-suppressed by the addition of the free-radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(-79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5—dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free-radical processes in a second-order process with an overall k ≃ 3 × 108 exp(-122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (-118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(-77 kJ/mol RT), 1.7 × 105 exp(-89 kJ/mol RT), and 3.1 × 109 exp(- 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free-radical process and by isomerization of COT.

Notes: The product quantum yields in the photolysis of 2,2,4,4-tetramethyl-3-pentanone have been measured in homogeneous solvents of different viscosities, in micellar solutions of cetyltrimethylammonium chloride and sodium dodecyl sulfate, and in dioctadecyl ammonium chloride vesicles.The product quantum yield in n-heptane was found to be 1. This value decreases to 0.5 in paraffin oil as a consequence of geminate recombination. In the presence of free radical scavengers, the extent of geminate disproportionation can be evaluated from the yields of isobutene and 2,2-dimethyl propionaldehyde. From these yields and the geminate recombination yields the total amount of geminate processes and the disproportionation-to-combination ratio for caged radicals are estimated. It is found that micelles provide the most efficient cages. In these media only about 10% of the radicals avoid cage processes. The disproportionation-to-combination ratio of tert-butyl and pivaloyl radicals was found to be extremely media dependent. The measured values ranged from about 0.2 in paraffin oil to 0.8 in cetyltrimethylammonium chloride micelles.

Notes: Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300-1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.

Notes: The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8-94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:The temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 /k_2 = (1.099 \pm 0.015)\exp [(429 \pm 2)/T] $$ $$ k_1 /k_r = (1.422 \pm 0.026)\exp [(1113 \pm 3)/T] $$ $$ k_2 /k_r = (1.295 \pm 0.029)\exp [(684 \pm 3)/T] $$ $$ k_3 /k_r = (1.177 \pm 0.025)\exp [(717 \pm 4)/T] $$ $$ k_4 /k_r = (1.115 \pm 0.023)\exp [(732 \pm 2)/T] $$ $$ k_5 /k_r = (0.978 \pm 0.020)\exp [(985 \pm 2)/T] $$\end{document} and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.

Notes: The reaction between ozone and carbon monoxide was reinvestigated in the range of 80-160°C. The previously reported rate law -d[O3]/dt = ka[O3][CO] + kb[O3]2 was confirmed and simulated using a mechanism based on an impurity-initiated chain reaction. When the CO was sufficiently purified, kb tended to zero and ka reduced to the value expected for the thermal decomposition of O3. Subsequent reactions of O atoms with CO produced chemiluminescence which was used to measure k3 for \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm O}\,\, + \,\,{\rm CO}\,\,\mathop {\longrightarrow}\limits^{\rm 3} \,\,{\rm CO}_{\rm 2} \left( {^3 B_2 } \right) $$\end{document} as 10-14.0±0.3 exp[-(1630 ± 325)/T] cm3 molecule-1 s-1. The implications of this are discussed.

Notes: The thermal decomposition of azoisopropane (AIP) was studied by detailed product analysis in the temperature and pressure intervals 498-563 K and 0.67-5.33 kPa. Besides the predominant termination and hydrogen-abstraction reaction of the 2-propyl radical, the decomposition is characterized by a very short chain process. The following rate constants were determined from the measurements\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{rcl} \log (k_1 {\rm /s}^{ - 1} ) &=& (16.3 \pm 0.2) - (199.9 \pm 1.6){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_4 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (4.1 \pm 0.3) - (52.5 \pm 3.0){\rm kJ mol}^{ - 1} /2.3RT \\ \log (k_5 /k_3^{1/2} {\rm dm}^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm mol}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. \kern-\nulldelimiterspace} 2}} ) &=& (2.4 \pm 0.1) - (27.6 \pm 1.3){\rm kJ mol}^{ - 1} /2.3RT \\ k_2 /k_3 &=& 0.51 \pm 0.02 \end{array}$$\end{document} for the following reactions:

Notes: Chlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3-chloropropene, cis- and trans-1-chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.

Notes: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254-425 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule-1 S-1): k1 = (1.33 ± 0.29) × 10-11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10-12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10-11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.

Notes: The reactions of ground-state S(3PJ) atoms with thiirane, methylthiirane, and trans-2,3-dimethylthiirane have been studied by flash photolysis-VUV kinetic absorption spectroscopy. From the analysis of the S(3PJ) decay plots the following rate constants were determined: (1.4 ± 0.2) × 1013, (2.7 ± 0.3) × 1013 and (4.0 ± 0.2) × 1013 (in cm3 mol-1 s-1 units) for thiirane, methylthiirane and trans-2,3-dimethylthiirane, respectively, showing an upward trend with increasing methylation.

Notes: NO Abstract.

Notes: An examination of the results of measurements of the forward and reverse rate constants for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm H} + {\rm C}_{\rm 2} {\rm H}_{\rm 6} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {\rm H}_{\rm 2} + {\rm C}_{\rm 2} {\rm H}_{\rm 5} $$\end{document} shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol-1. This system therefore provides further support for the recent measurement of this quantity.

Notes: The very low pressure reactor (VLPR) technique has been used to measure the bimolecular rate constant of the title reaction at 300 K. The rate constant is given by log k1 (1/mol s) = (11.6 ± 0.4) - (5.9 ± 0.6)/θ the equilibrium constant has also been measured at the same temperature and is given by K1 = (5.6 ± 1) × 10-3 and hence log k-1 (1/mol s) = 9.5 ± 0.1. The results show that the reaction Br + t—C4H9 → HBr + i—C4H8 is unimportant under the present experimental conditions. Assigning the entropy of t-butyl radical to be 74 ± 2 eu which is in the possible range, the value of K1 gives ΔH°f (t-butyl) = 9.1 ± 0.6 kcal/mol-1. This yields for the bond dissociation, DH° (t-butyl-H) = 93.4 ± 0.6 kcal/mol. Both of these values are found to be in good agreement with recent VLPP studies.

Notes: Kinetics of the basic hydrolysis of glyceryl trinitrate (TNG) were investigated in CO2-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. TNG hydrolyzed via second-order reaction at 25°C, 18°C, and 10°C. The activation energy of the hydrolysis reaction of TNG was calculated from the kinetic data and found to be equal to 27.53 kcal/mol. The major products of the hydrolysis of TNG in solution of calcium hydroxide were calcium nitrate and calcium nitrite, accounting for approximately 50% of the degradation products. The minor identified products such as calcium oxalate and nitrate esters amounted to approximatey 6% of the products. The remaining 30% of the isolated products was a mixture of calcium formate, a nitrate ester, and unidentified volatiles, polymerlike substances, and other organic residue.

Notes: Results obtained from the photolysis of ketene with acetylene strongly support the formation of C3H3 radicals in the title reaction. Stationary state studies are interpreted in terms of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_3 {\rm H}_{\rm 4}^{\rm *} \buildrel3\over\rightarrow{\rm C}_3 {\rm H}_3^ \cdot + {\rm H}^ \cdot$$\end{document} with a rate constant (109.8 s-1) which is compared to RRKM predictions. In pulsed laser induced decomposition experiments, recombination products involving C3H3 have been detected (some for the first time) and their formation modeled using step (3) with the same rate constant.

Notes: A readily applicable empirical formula is obtained for the collisional efficiency for energy transfer between a highly vibrationally excited reactant and a seasoned (usually quartz) wall, in terms of the molecular weight, potential well depth and dipole moment of the reactant. This expression is used to examine corrections due to nonunit wall collision efficiency in the high-pressure rate parameters obtained from very low-pressure pyrolysis experiments. It is found that these corrections are up to ca. ±5 kJ/mol in the high-pressure activation energy and a factor of ca. 2 in the high-pressure frequency factor, for molecules with molecular weight less than ca. 100 and where experiments are carried out at temperatures exceeding 1000 K.

Notes: The rate constants for reactions (4) and (5) were determined at room temperature by pulsed laser photolysis and time resolved mass spectrometry. A description of the experimental setup is given. CFCl2O2 radicals were generated by photolysis of CFCl3 at 193 nm in the presence of an excess of oxygen, using an excimer laser. The rate constant for reaction (4), determined under different experimental conditions is: \documentclass{article}\pagestyle{empty}\begin{document}$$k_4 = 1.6{\rm }(\pm 0.2) \times 10^{ - 11} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1}$$\end{document} The rate constant of reaction (5) was determined in the pressure range of 1-12 torr, using oxygen as the buffer gas. The reaction is in its fall-off region and the parameters determined by using the semiempirical method of Troe, taking Fc = 0.6 are: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k(0) = 3.5{\rm }(\pm 0.5) \times 10^{ - 29} {\rm cm}^{\rm 6} \cdot {\rm molecule}^{ - 2} \cdot {\rm s}^{ - 1} \\ k(\infty) = 6.0{\rm }(\pm 1.0) \times 10^{ - 12} {\rm cm}^{\rm 3} \cdot {\rm molecule}^{ - 1} \cdot {\rm s}^{ - 1} \\ \end{array}$$\end{document} The value of k(∞) is obtained from the low-pressure measurements and therefore the uncertainty on the actual high-pressure limit is higher than the error limits quoted above. The results are compared with those reported for similar reactions.

Notes: Potassium persulfate oxidizes triphenylphosphine to triphenylphosphine oxide in 60% aqueous acetonitrile. It has been suggested that the oxygen of the product, triphenylphosphine oxide, might originate from solvent water, following nucleophilic attack on an intermediate phosphonium ion. We have investigated the origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate in 60% aqueous acetonitrile containing 20% [18O]water. The product was analyzed by using the 18O isotope effect in 31P NMR spectroscopy. The magnitude of the 18O isotope-induced shift was determined by synthesizing triphenylphosphine [18O]oxide and was found to be 0.038 ppm upfield. The product of the oxidation reaction in 20% [18O]water displayed no 18O isotope effect. The origin of the oxygen in the oxidation reaction is the persulfate ion, consistent with an alternative mechanism involving nucleophilic attack by water at the sulfur atom of a phosphonium peroxysulfate intermediate.

Notes: It is shown how kinetic electron spin resonance spectroscopy with intermittent radical generation can be used to obtain rate constants of various simultaneous reactions in systems containing more than one kind of transient radicals. The technique is applied to reactions of tert-butyl [(CH3)3Ċ] and isopropylol [(CH3)2ĊOH] radicals generated by photolysis of di-tert-butyl ketone and acetone in 2-propanol/acetone mixtures. It yields the rates of generation of the two radicals, the rate constants for their self- and crossterminations and for the reaction of tert-butyl with 2-propanol. The extent of diffusion control of the termination constants is discussed.

Notes: Trifluoro-t-butoxy radicals have been generated by reacting fluorine with 2-trifluoromethyl propan-2-ol: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \dot F} + {\rm CF}_3 {\rm C}({\rm OH})({\rm CH}_3)_2 \to {\rm HF} + {\rm CF}_3 {\rm C}({\rm \dot O})({\rm CH}_3)_2 $$\end{document} Over the temperature range 361-600 K the trifluoro-t-butoxy radical decomposes exclusively by loss of the —CF3 group [reaction (-2)] rather than by loss of —CH3 group [reaction (-1)]: The limits of detectability of the product CF3COCH3, by gas-chromatographic analysis, place a lower limit on the ratio k-2/k-1 of ca. 75. The implications of these results in relation to the reverse radical addition reactions to the carbonyl group are discussed along with the thermochemistry of the reactions.

Notes: The gas-phase reaction of CF3 with HCN has been examined over a wide conversion range using CF3I as a thermal and photolytic source of radicals. Quantitative and qualitative results show a significant increase of the specific rate constant for the hydrogen abstraction reaction relative to CF3 recombination when reaction is carried out under ultraviolet irradiation. This “extra” formation of the reaction product, CF3H, has been assigned to the participation of iodine in this system through the formation of a (I-HCN) intermediate. Arrhenius parameters obtained for the addition mechanism of I to HCN do not seem to conform to a single reaction step, on the contrary, they correspond to a more complex reaction scheme.

Notes: Small low residence time flow tube reactors made of alumina and used as molecular beam sources are described. In these reactors, gas mixtures are rapidly heated and brought to reaction. The composition of the gas leaving the reactor is analyzed by molecular beam mass spectroscopy. For quantitative simulation of the reacting gas flow, the theory of one-dimensional compressible flow with friction, heat transfer, and chemical reaction is brought into a form suitable for practical computation. The system has been applied to study the thermal decompositions of O3 and N2O. The experimental results on both reactions can be well modeled by homogeneous reaction mechanisms with accepted rate constants. Heterogeneous reaction steps are shown to be unimportant.

Notes: The yield of benzene in the reaction of 1,4- and 1,3-cyclohexadiene with OH radicals in the presence of oxygen was determined using H2O2 and CH3ONO as OH radical sources. Both in the H2O2 and the CH3ONO systems, the yield of benzene from 1,4-cyclohexadiene was 15.3% and the yield from 1,3-cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per C—H in cyclohexadiene was determined to be 3.8 × 10-12 cm3 molecule-1 s-1. The branching ratio of the hydrogen abstraction to overall reaction for 1-butene and 1-pentene was estimated to be (25-14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts [4].

Notes: The photolysis of carbon tetrachloride in the presence of a number of organosilicon compounds has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the organosilane. Arrhenius parameters for hydrogen atom transfer were determined relative to those for trichloromethyl radical combination. The activation energies for the reaction of methyl, trifluoromethyl, and trichloromethyl radicals with organosilicon compounds are compared and the results rationalized in terms of polar effects.

Notes: Calculations of low-pressure limit, third-order rate constants are presented for the association reactions A + O2 + N2 and A + OH + N2 (A = Li, Na, K) over the temperature range 200-2000 K and a comparison is made with the available experimental data.

Notes: The photooxidation of formaldehyde in CH2O—O2, oxygen-lean mixtures was studied in the temperature range 298-378 K. H2 and CO formation and the loss of O2 proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO2 + CH2O ⇄ HO2CH2O (5) is now assumed to be reversible and ΔH5° is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H2 and CO and of the consumed O2 remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH2O → H2O HCO† (7), HO + CH2O → H2O + HCO (8) and HO + CH2O → HOCH2O (9) are temperature independent.

Notes: The kinetics of OH reactions with 1-4 carbon aliphatic thiols have been investigated over the temperature range 252-430 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2-4.6 × 10-11 cm3 molecule-1 s-1, -Eact = 0.6-1.0 kcal/mol, A = 0.6-1.2 × 10-11 cm3 molecule-1 s-1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.

Notes: The oxidation of inositol by quinquevalent vandadium in acid medium is a first-order reaction both in vanadium (V) and inositol. The stoichiometry of the reaction is consistent with the use of two equivalents of vanadium (V) per mole of inositol with the formation of one mole of inosose. The reaction is catalyzed both by sulfuric and perchloric acid, but the rate is faster in sulfuric acid than in perchloric acid. In 1M-6M perchloric acid solutions the reaction has shown a variable order in H+, but in solutions of 2M-5M sulfuric and perchloric acid of constant ionic strength, the rate has a linear dependence on [H+]2. There is also a linear correlation between the rate and bisulfate ions in sulfuric acid at constant hydrogen ion concentration. The energy of activation is found to be 19 kcal/mole and a negative entropy value of - 14 e.u. A suitable mechanism, consistent with the kinetics in 2M-5M acid solutions, is suggested and the values of various rate constants are evaluated.

Notes: Very strong laser emission at 5 μm was detected when SO2 and CHBr3 were flash photolyzed in the vacuum ultraviolet (λ ≥ 165 nm) in the presence of a large amount of diluent (SF6, He, or Ar). About 110 vibration-rotation transitions ranging from Δv = 18 → 17 to 3 → 2, except 16 → 15, were identified. The primary reactions leading to the CO stimulated emission are as follows: The product analysis results and the variation of laser intensity with flash energy and SO concentration indicate that the following side reactions are also occurring. Addition of a small amount of O2 enhances the laser output by both eliminating these side reactions and simultaneously producing vibrationally excited CO via reaction (8), which has been previously shown to generate CO stimulated emission. The effects of various reactive (NO and H2) and inert (He, Ar, SF6, CO, N2, N2O, and CO2) gases have been examined. All additives (P ≤ 20 torr), except NO and H2, increase the total laser output. N2O enhances the power most efficiently, whereas CO, N2, and CO2 are less effective and have similar efficiencies. The enhancement of the laser intensity by these near-resonant gases is ascribed to the depletion of CO population at lower levels which thus increases the rates cascading from higher levels. NO and H2 quench the laser output by chemically reducing the concentration of the CH radical.

Notes: A kinetic study of lead atoms in the spin orbit states, Pb(63P1) and Pb Pb(63P2), 0.969 and 1.320 eV, respectively, above the 63P0 ground state, has been carried out by atomic absorption spectroscopy. The electronically excited lead atoms were generated by the pulsed irradiation of lead tetraethyl and monitored photoelectrically by time-resolved attenuation of resonance radiation. The decay of the two atomic states has been studied in the presence of He, Ar, H2, D2, N2, O2, CO, NO, CO2, N2O, CH4, C2H4, C2H2 CF4, SF6, and PbEt4, and rate constants for the collisional quenching by these gases are reported. The resulting data are compared with those for the deactivation of other atomic spin orbit states of comparable energy. In general, the higher energy state, Pb(63P2), is found to be deactivated more rapidly. It would appear that the magnitude of the electronic energy to be transferred on collision governs the rates of quenching, at least where a weak interaction potential is involved, and that for most gases, deactivation of Pb(63P2) proceeds via Pb(63P1).

Notes: The preparation and characterization of the iron(II) complex of the hexadentate Schiff base ligand NN‴-bis-[α-(2-pyridyl)benzylidene]triethylenetetramine are reported. Kinetic patterns and rate constants for aquation of this complex, and for its reactions with hydroxide, cyanide, and peroxodisulphate have been determined. Activation parameters for the reaction with cyanide, in aqueous solution, are ΔH

Notes: Methods are discussed for the production and detection of the hydroperoxyl radical for use in gas phase kinetic studies. Rate constants for gas phase reactions of the hydroperoxyl radical with itself, H2, H2O, CO, NO, SO2, O3, C2H6, C3H8, i-and n-C4H10, C2H4, i-C4H8, HCHO, C2H5CHO, n-C3H7CHO, Br, O, OH, and H are critically evaluated. Recommended or estimated rate constant expressions with associated error limits are given applicable over specified temperature ranges (normally 300-1000°K). The reactivity of HO2 compared with OH, O, H, F, Cl, Br, CH3, and CH3O is presented in tabular form and the implications for atmospheric chemistry are discussed.

Notes: The pyrolysis of C6F5I has been studied by the toluene carrier method over the temperature range of 900-978°K with contact times of 0.4-2.0 seconds and total pressures of 11.2-19.5 torr. Percent decomposition ranged from 8.6 to 97.7%. With toluene-to-C6F5I molar ratios of greater than 150, 85-100% of the C6F5 released abstracts a hydrogen atom from toluene to produce C6F5H. No significant quantities of I2 were observed and the only major gaseous product was HI. Within the limits of the experimental method the decomposition of C6F5I was first order and homogeneous.Least squares analysis of log k1 and 103/T(C6F5I → C6F5 + I) values gives \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}\,k_1 ({\rm s}^{- 1}) = 15.9 - 69,200/4.576T $$\end{document} while a weighted line of best fit yields. \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}\,k_1 ({\rm s}^{- 1}) = 15.4 - 67,000/4.576T$$\end{document} Based on this latter equation D[C6F5—I] at 298°K is estimated as 66.2 kcal/mole.

Notes: The kinetics of the gamma-radiation-induced free radical chain reaction in solutions of C2Cl3F in cyclohexane (RH) was investigated over a temperature range of 87.5-200°C. The following rate constants and rate constant ratios were determined for the reactions: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (2a)}} & {{\rm R} + {\rm C}_{\rm 2} {\rm Cl}_{\rm 3} {\rm F} \to {\rm RCClFCCl}_{\rm 2}} \\ \end{array}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(2{\rm b})} & \to \\ \end{array}{\rm RCCl}_{\rm 2} {\rm CClF}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c}{{\rm (3a)}} & {{\rm RCClFCCl}_{\rm 2} \to {\rm RCF}}\\ \end{array}{\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}}{\rm CCl}_{\rm 2} + {\rm Cl}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (4a)}} & {{\rm RCClFCCl}_{\rm 2} + {\rm RH} \to {\rm RCClFCCl}_{\rm 2} {\rm H} + {\rm R}} \\ \end{array}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k_{2a} ({\rm mole}^{{\rm - 1}} 1.\,{\rm sec}^{{\rm - 1}}) = (8.64 \pm 0.35) - (6.38 \pm 0.41)/\theta ^1$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k_{{\rm 2b}} /k_{{\rm 2a}} = (- 0.03 \pm 0.15) - (2.39 \pm 0.28)/\theta$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm (}k_{3{\rm a}} /k_{4{\rm a}})({\rm mole}\,1.^{{\rm - 1}}) = (6.17 \pm 0.10) - (10.14 \pm 0.18)/\theta$$\end{document} In competitive experiments in ternary solutions of C2Cl4 and C2Cl3F in cyclohexane the rate constant ratio k2c/k2a was determined \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (2c)}} & {{\rm R} + {\rm C}_{\rm 2} {\rm Cl}_{\rm 4} \to {\rm RC}_{\rm 2} {\rm Cl}_{\rm 4}} \\ \end{array}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k_{{\rm 2c}} /k_{{\rm 2a}} = (0.13 \pm 0.06) - (1.20 \pm 0.12)/\theta$$\end{document} By comparing with previous data for the addition of cyclohexyl radicals to other chloroethylenes it is shown that in certain cases the trends in activation energies for cyclohexyl radical addition can be correlated with the C—Cl bond dissociation energies in the adduct radicals.

Notes: The substitution of N-alkyl substituted ethylenediamines for chloride ions in the rapidly equilibrating system \documentclass{article}\pagestyle{empty}\begin{document}$${\rm PdCl}_{\rm 4} ^{{\rm 2 - }} {\rm + H}_{\rm 2} {\rm O}\rightleftharpoons{\rm PdCl}_{\rm 3} ({\rm H}_2 {\rm O)}^{\rm - } + {\rm Cl}^{\rm - }$$\end{document} has been investigated in aqueous acid medium. The kinetic data can be accommodated by the general rate law \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \left\{ {\frac{k}{{\left[{{\rm H}^{\rm + }} \right]}} + \frac{{k'}}{{\left[{{\rm H}^{\rm + } } \right]\left[{{\rm Cl}^{\rm - } } \right]}}} \right\}\left[{{\rm N}_{\rm n} {\rm N}_{\rm m} {\rm en}} \right]_{{\rm total}}$$\end{document} where n = 0, 1, or 2 and m = 0, 1, or 2, depending on whether none, one, or two methyl groups are attached to the two nitrogen atoms of ethylenediamine. Reaction with the most heavily substituted ethylenediamine, namely, N2N2en discloses a change of the mentioned rate law to \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \left\{ {\frac{{k''}}{{\left[{{\rm H}^{\rm + } } \right]}} + \frac{{k'''\left[{{\rm Cl}^{\rm - } } \right]}}{{\left[{{\rm H}^{\rm + } } \right]}}} \right\}\left[{{\rm N}_{\rm 2} {\rm N}_{\rm 2} {\rm en}} \right]_{{\rm total}}$$\end{document} on going from a lower to a higher chloride ion concentration range. This change in the mathematical form of the rate law can be explained in terms of an ion-pair association of N2N2enH+ and free chloride ions.

Notes: An inhibitor method for measuring the initiation rate is proposed for the system Fe3+ + H2O2. C(NO2)4 was used as inhibitor. The number of chains terminated by one C(NO2)4 molecule was estimated in specific photochemical experiments and found to be unity. The initiation appeared to involve two processes. The first is proportional to the first power of ferric ion concentration, and the second to the second power. The rate constants and activation energies of these processes are determined. Allowance for the second initiation process permitted qualitative and quantitative description of various reported data on H2O2 decomposition rates over a wide range of Fe3+, H2O2, and H+ concentrations.

Notes: The effect of the addition of hydrogen chloride on the photolysis of carbon tetrachloride in the presence of cyclohexane has been investigated in a companion paper. The data enable the rate constant ratio k8/(k5)1/2 to be determined. Since k-8 is well established, k5 can be estimated from known thermochemical data. The validity of the thermochemical derivation is checked by applying it to trifluoromethyl radicals. The photolysis of bromotrichloromethane and carbon tetrachloride in the presence of hydrogen chloride has been investigated over a range of temperatures. From these results and assuming reaction (5) has no activation energy, Arrhenius parameters for reaction (8) have been determined: The activation energies for the reaction of methyl, trichloromethyl, and trifluoromethyl radicals with hydrogen chloride are compared, and at first sight surprising results are rationalized in terms of relative electronegativity.

Notes: Measurements of rates of oxygen absorption and steady-state peroxy radical concentrations for the autoxidation of tetralin in the presence of tert-butyl hydroperoxide have shown that the rate constant for reaction of the tert-butylperoxy radical with tetralin at 60°C is approximately 11.0 M-1 s-1. This rate constant is about a factor of 4 larger than the value recently reported by Niki, Okayasu, and Kamiya for this reaction.The present work emphasizes that great care should be taken when the hydroperoxide method is used to estimate cross-propagation rate constants for a substrate as reactive as tetralin at a temperature as high as 60°C.

Notes: The decomposition of acetylenedicarboxylic acid in acetophenone was studied in the temperature range of 100-130°C. The rate constants and activation parameters for the consecutive pair of first-order steps (each yielding carbon dioxide) were calculated. Hydrogen kinetic isotope effects were also studied. Comparisons were made with the decompositions of oxalic acid and malonic acid. An intramolecular H—C transfer is believed to be the main part of the reaction coordinate in addition to the C—C bond breaking.

Notes: Chloroethanes react with aqueous caustic to yield either elimination or substitution products. The reaction rates were measured for the dichloroethanes, trichloroethanes, tetrachloroethanes, and pentachloroethane between 283 and 353°K. The constants of HCl eleminations referring to the rate equation \documentclass{article}\pagestyle{empty}\begin{document}$$r = k[{\rm OH}^{\rm - }][{\rm dissolved \,substrate]}$$\end{document} are given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,2 - C}_{\rm 2} {\rm H}_{\rm 4} {\rm Cl}_{\rm 2} {\rm }\,k = 10^{10.99 \pm 0.03} \exp (- 23,000 \pm 50RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,2 - C}_{\rm 2} {\rm H}_{\rm 3} {\rm Cl}_{\rm 3} {\rm}\,k = 10^{13.99 \pm 0.03} \exp (- 22,400 \pm 50/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,1,2 - C}_{\rm 2} {\rm H}_{\rm 2} {\rm Cl}_{\rm 4} {\rm }\,k = 10^{15.45 \pm 0.14} \exp (- 25,800 \pm 210/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm 1,1,2,2 - C}_{\rm 2} {\rm H}_{\rm 2} {\rm Cl}_{\rm 4} {\rm }\,k = 10^{16.40 \pm 0.05} \exp (- 22,550 \pm 70/RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_{\rm 2} {\rm HCl}_{\rm 5} {\rm }\,k = 10^{12.50 \pm 0.08} \exp (- 15,200 \pm 110/RT)$$\end{document} all rate constants being in 1./mole·s and R in cal/mole· deg.With ethyl chloride, 1,1-dichloroethane, and 1,1,l-trichloroethane, the elimination is not observed and a slow substitution takes place. The influence of chlorine substituents on both sides of the molecule on mechanism and rate parameters is discussed.

Notes: The occurrence of anchimeric assistance in the vapor-phase thermolysis of anti- and syn-7-acetoxy-7-methylnorbornene and 7-acetoxy-7-methylnorborane has been investigated. The relative rates of thermolysis were found to be 1.9, 0.87, and 1.0, respectively. The nature of the transition state for ester thermolysis is discussed in light of the small amount of anchimeric assistance found in the thermolysis of the anti-isomer.

Notes: The heats of formation of C3 and C4 alkyl nitrites (RONO) have been determined via their heats of combustion by bomb calorimetry, thereby providing a complete set of values of ΔHºf for C1-C4 alkyl nitrites. The experimental values are in excellent agreement with values derived from group additivity rules. For branched compounds these calculations involve corrections for gauche interactions. In these cases, the gauche interactions are reflected in the activation energies E1 determined by recent kinetic studies, required for breaking the RO-NO bond. The heats of formation of the alkoxy radicals involved together with ΔHºf(NO) = 21.6 kcal/mole leads to the result D(RO-NO) = 41.5 ± 1 kcal/mole. The concordance between D(thermochemical) and D(kinetic), unlike previous kinetic studies, implies that E2 = 0 ± 1 kcal/mole.

Notes: The reactions where Y = CH3 (M), C2H5 (E), i—C3H7 (I), and t—C4H9 (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NMBO}} = - {{\left( {26530 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26530 \pm 80} \right)} {4.576T + \left( {6.05 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.05 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XMBO}} = - {{\left( {28910 \pm 130} \right)} \mathord{\left/ {\vphantom {{\left( {28910 \pm 130} \right)} {4.576T + \left( {6.32 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.32 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NEBO}} = - {{\left( {26150 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {26150 \pm 120} \right)} {4.576T + \left( {5.85 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.85 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XEBO}} = - {{\left( {28560 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {28560 \pm 120} \right)} {4.576T + \left( {6.07 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.07 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NIBO}} = - {{\left( {26560 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26560 \pm 80} \right)} {4.576T + \left( {5.57 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.57 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XIBO}} = - {{\left( {28350 \pm 100} \right)} \mathord{\left/ {\vphantom {{\left( {28350 \pm 100} \right)} {4.576T + \left( {5.47 \pm 0.04} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.47 \pm 0.04} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NTBO}} = - {{\left( {28920 \pm 50} \right)} \mathord{\left/ {\vphantom {{\left( {28920 \pm 50} \right)} {4.576T + \left( {5.86 \pm 0.02} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.86 \pm 0.02} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XTBO}} = - {{\left( {32890 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {32890 \pm 120} \right)} {4.576T + \left( {6.19 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.19 \pm 0.05} \right)}} $$\end{document} The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.

Notes: The technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time-resolved detection of the 1.3-μm emission from I*(2P1/2) has been used to measure the rate constants for deactivation of I* by CH3I, C2H5I, CF3I, and CH4. The recommended values are (2.76± 0.22) × 10-13, (2.85 ± 0.40) × 10-13, (3.5 ± 0.5) × 10-17, and (7.52 ± 0.12) × 10-14, respectively, in units of cm3 molecule-1 S-1.

Notes: The reactions of labeled N15NO+ with CO, NO, O2, 18O2, N2, NO2, and N2O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.

Notes: The reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 - initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol): \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 3} \mathop {\longrightarrow}\limits_{\left( {\rm M} \right)}^{39} {\rm H}\,\, + \,\,{\rm C}_{\rm 2} {\rm H}_{\rm 2} } & {\log k\left( {1\,{\rm atm,}\,{\rm 1300}\,{\rm K}} \right)\, = \,5.2\, + \,0.3\,s^{ - 1} } \\ \end{array} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm C}_{\rm 2} {\rm H}_{\rm 4} \, + \,\mathop {{\rm C}_{\rm 2} }\limits^. \,\mathop {\longrightarrow}\limits^{17} \,\mathop {{\rm C}_{\rm 4} }\limits^. {\rm H}_{\rm 7} } \hfill & {E\, \ge \,2\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}\,} \hfill \\ {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 5} \, + \,{\rm C}_{\rm 6} {\rm H}_{\rm 6} \,\mathop {\longrightarrow}\limits^{40} \,\mathop {{\rm C}_{{\rm 12}} }\limits^. {\rm H}_{{\rm 11}} } \hfill & {E\, = \,11\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}} \hfill \\ \end{array} $$\end{document}

Notes: The kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH⋅), the dismutation of benzophenone radical anions, the disproportionation between BPH⋅ and stable nitroxyl radicals, (), and the electron transfer have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n-hexane is controlled by diffusion with 2k1 ≃ kdiff. In aliphatic alcohols and toluene, which form solvation complexes with BPH⋅, reaction (1) is diffusion-enhanced and activation-controlled, respectively, with 2k1 〈 kdiff. In a viscous solvent such as 1-propanol-glycerol mixture (100 ≲ η ≲ 450 cP) reaction (1) is diffusion-controlled. Reaction (2) in alkaline 1-propanol and alkaline 1-propanol-glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water-glycerol and 1-propanol-glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k3 (k4) are 2-6 times as small as the corresponding kdiff values due to the low steric factor of the reactions (therefore called pseudodiffusion-controlled reactions). The theoretical estimates of k3 (k4) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.

Notes: The approximations developed to determine the energy distribution function of molecules activated above energy decomposition threshold, from experimental data, have been tested. The approach involved the theoretical (RRKM) calculations of “pseudoexperimental” data for a variety of activated energy distributions. (Single or double Gaussian representations were used in all cases.) Subsequently the algorithms mentioned were applied in order to recuperate the original (i.e., input) energy distributions from these pseudoexperimental data. The results obtained provide strong evidence in favor of the validity of the algorithms and illustrate the necessary requirements for their applications. A trend toward lower accuracy as the energy distributions move to higher energies has been observed. Evidence of the influence of the distribution width is also reported. The origins of the approximation errors have been studied, and ways for further improvement are suggested.

Notes: The autooxidation of retinyl acetate and methyl retinoate was investigated in chlorobenzene at 45°C. The rates of thermal initiation in the retinyl acetate solutions were measured, and a value was determined of the rate constant for the reaction of oxygen with retinyl acetate (RH + O2 → R· + HO2·): kio = (1.3 ± 0.2) × 10-5 L/mol · s. The number of moles of oxygen absorbed per mole of polyene depends on the substrate concentration. A kinetic scheme for the methyl retinoate autooxidation was proposed which takes into account the isomerization of primary peroxy radicals, and the rate constants for different elementary reactions were estimated. The partial rate constant for “allylic” hydrogen abstraction from retinyl acetate was estimated to be ≥ 1.65 × 103 L/mol · s. A probable propagation sequence was proposed for the autooxidation of retinyl acetate.

Notes: Rate constants for the self- and cross-termination of the isopropylol radical [(CH3)2ĊOH] and its anion [(CH3)2ĊO-] in aqueous solution are determined by kinetic electron spin resonance. Whereas the self-termination of the neutral radical occurs close to the diffusion-controlled limit, the cross- and self-terminations involving the anion are slower and reflect effects of charge repulsion and steric constraints by solvation.

Notes: The unimolecular decomposition of methyl nitrite in the temperature range 680-955 K and pressure range 0.64 to 2.0 atm has been studied in shock-tube experiments employing real-time absorption of CW CO laser radiation by the NO product. Computer kinetic modeling using a set of 23 reactions shows that NO product is relatively unreactive. Its initial rate of production can be used to yield directly the unimolecular rate constant, which in the fall-off region, can be represented by the second-order rate coefficient in the Arrhenius form: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 10^{17.90 \pm 0.21} \exp (- 17200 \pm 400/T){\rm cm}^{\rm 3} {\rm mol}^{ - 1} {\rm s}^{ - 1}$$\end{document} A RRKM model calculation, assuming a loose CH3ONO≠ complex with two degrees of free internal rotation, gives good agreement with the experimental rate constants.

Notes: Using a relative rate technique, rate constants for the gas phase reactions of the OH radical with n-butane, n-hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1-butene, 1.19 ± 0.06; 1-pentene, 1.19 ± 0.05; 1-hexene, 1.40 ± 0.04; 1-heptene, 1.51 ± 0.06; 3-methyl-1-butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09; cis-2-butene, 2.13 ± 0.05; trans-2-butene, 2.43 ± 0.05; 2-methyl-2-butene, 3.30 ± 0.13; 2,3-dimethyl-2-butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3-butadiene, 2.53 ± 0.08; 2-methyl-1,3-butadiene, 3.81 ± 0.15; n-butane, 0.101 ± 0.012; and n-hexane, 0.198 ± 0.017. From a least-squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10-11 cm3 molecule-1 s-1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self-consistent data set for the reactions of OH radicals with a large number of organics at room temperature.

Notes: The kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4-Na2SO4-NaClO4 at 25.0°C and ionic strength 2.0 mol dm-3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{(b[{\rm HSO}_4^ -] + c[{\rm HSO}_4^ -]^2 + [{\rm H}^ +]){\rm [HL]}}}{{\{ f_1 [{\rm HSO}_4^ -]^3 + d_1 [{\rm HSO}_4^ -] + e_1 [{\rm HSO}_4^ -]^2){\rm }[{\rm H}^ +]\} + A'[{\rm HL}]}}$$\end{document} where kobs indicates the observed pseudo-first-order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO4-] concentrations. Moreover, three equilibria involving cerium(IV) and HSO4- (or SO42-) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.

Notes: A kinetic study of oxidation of hydroxylamine by bromate ion in acid sulfate solution using spectrophotometric and potentiometric methods is reported. Oxidation of hydroxylamine to nitrate is quantitative and followed competitive, consecutive, and auto catalytics steps characterized by induction periods. In the slow rate limiting step, hydroxylamine on reaction with HOBr (k1′) forms an intermediate I, which further reacts fast with second molecule of HOBr (k2′) giving nitrite. Nitrite reacts with HOBr (k3′) yielding the final product nitrate. Nitric acts as an autocatalyst also and its initial addition decreased the induction periods. In excess of hydrogen ion concentration all the reaction steps follow second-order kinetics. All the second-order rate constants are reported and the reaction mechanism is proposed.

Notes: Mixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750-2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration - time histories. The early-time NH3 and OH concentration profiles were sensitive to the rate constants of the reactionsleading to the following best-fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(-4470/T) and k3 = 1013.91±0.2 exp(-4230/T) cm3 mol-1 s-1. The results of this study combined with previous low-temperature data suggest a significant non-Arrhenius behavior for both k2 and k3.

Notes: The thermal decomposition of azoisopropane (AIP) was studied in the presence of various quantities of propylene in the temperature and pressure intervals 498-553 K and 3.33-5.33 kPa. The inhibition functions relating to formation of the products were determined; these proved a good basis for interpretation of the formation of the secondary decompositon products of AIP. The experimental data support the conception that the βμ radical - radical reactionoccurs. The product of this is not stable; its decomposition is one of the sources of the secondary products. The ratio of the rate constants was determined for the following reactions:

Notes: The photooxidation of acrylonitrile, methacylonitrile, and allylcyanide in the presence of NO was studied in parts per million concentration using the long-path Fourier transform IR spectroscopic method. The stoichiometry of the OH radical initiated oxidation of methacrylonitrile was established as \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm C}\left( {{\rm CH}_{\rm 3} } \right){\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + CH}_{\rm 3} {\rm COCN + 2NO}_{{\rm 2}} + \left( {{\rm OH}} \right) $\end{document}. The yield of HCHO for acrylonitrile and allylcyanide was found to be ca. 100 and 80%, and the stoichiometric reactions were assessed to proceed, \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + HCOCN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCH}_{\rm 2} {\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{0.8} {\rm HCHO + HCOCH}{\rm 2} {\rm CN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document}, respectively. These results revealed that the reaction mechanism for these unsaturated organic cyanides are analogous to that of olefins.

Notes: Rates and thermodynamic data have been obtained for the reversible self-termination reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm R}^ \cdot + {\rm R}^ \cdot \mathop{\buildrel\longleftarrow\over\longrightarrow}^{2k1}_{2k_{-1}}D $$\end{document} Involving aromatic 2-(4′dimethylaminophenyl)indandione-1,3-yl (I), 2-(4′diphenylaminophenyl)indandione-1,3-yl (II), and 2,6 di-tert-butyl-4-(β-phthalylvinyl)-phenoxyl (III) radicals in different solvents. The type of solvent does not tangibly affect the 2k1 of Radical(I), obviously due to a compensation effect. The log(2k1) versus solvent parameter ET(30) curves for the recombination of radicals (II) and (III) have been found to be V shaped, the minimum corresponding to chloroform. The intensive solvation of Radical (II) by chloroform converts the initially diffusion-controlled recombination of the radical into an activated reaction. The log (2k-1) of the dimer of Radical (I) has been found to be a linear function of the Kirkwood parameter (ε - 1)/(2ε + 1), the dissociation rate increasing with the dielectic constant of the solvent. The investigation revealed an isokinetic relationship for the decay of the dimer of Radical (I), an isokinetic temperature β = 408 K and isoequilibrium relationship for the reversible recombination of Radical (I) with β° = 651 K. For Radical (I) dimer decay In(2k-1) = const + 0.8 In K, where K is the equilibrium constant of this reversible reaction. The transition state of Radical (I) dimer dissociation reaction looks more like a pair of radicals than the initial dimer. The role of specific solvation in radical self-termination reactions is discussed.

Notes: The thermal decomposition of SO2 and of the primary dissociation product SO have been studied in shock waves by the uv absorption technique. The controversy about SO2 dissociation data from uv absorption signals was resolved and attributed to the extensive overlap of SO2 and SO uv absorption spectra. The derived rate coefficients are k1/[Ar] = 1015.6 exp(-420 kJmol-1/RT) cm3mol-1 s-1 (temperature range 3000-5000 K) for SO2 dissociation, and k3/[Ar] = 1014.6 exp(-448 kJmol-1/RT) cm3 mol-1 s-1 (temperature range 4000-6000 K) for SO dissociation. Anomalously high values of the apparent collision efficiencies βc in SO2 dissociation are attributed to marked contributions from excited electronic states.

Notes: 5-Methyl-hexanone-2, 3-methyl-pentanone-2, and hexanone-2 have been decomposed in comparative rate single pulse shock tube experiments. The mechanism of decomposition involves the breaking of carbon-carbon bonds as well as molecular processes involving 6-center complexes. The following rate expressions at 1100 K have been obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} k(3{\rm - methyl - pentanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm sC}_4 {\rm H}_9 .) = 10^{16.4} \exp (- 38,300/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm iC}_4 {\rm H}_9 .) = 10^{16.6} \exp (- 40,600/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm iC}_4 {\rm H}_8) = 10^{12.56} \exp (- 31,600/T)/{\rm s} \\ k({\rm hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm C}_3 {\rm H}_6) = 10^{13.28} \exp (- 32,400/T)/{\rm s} \\ \end{array} $$\end{document} These results lead to ΔHf(CH3ĊO) = - 13.8 kJ and ΔHf(CH3COCH2·) = - 12.6 kJ at 300 K. They are compared with existing literature values and some generalizations are made with regard to the stability of carbonyl compounds.

Notes: Kinetics of the incorporation of mercury(II) ion in tetra (p-trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO3) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 103 M-1 s-1 and 7 ± 2 × 106 M-1 s-1, respectively. Kinetics of zinc(II) incorporation in tetra(p-trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady-state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.

Notes: The absolute rate constant for the OH + HCl reaction has been measured from 240 to 295 K utilizing the techniques of laser/flash photolysis-resonance fluorescence. The HCl concentrations were monitored continuously by ultraviloet and infrared spectrophotometry. The results can be fit to the following Arrhenius expression: \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (4.6{\rm } \pm {\rm }0.3){\rm } \times {\rm }10^{ - 12} \exp [- (500{\rm } \pm {\rm }60)/T{\rm cm}^3 /{\rm molecule} \cdot {\rm s}$$\end{document} The rate constant values obtained in this study are 20-30% larger than those recommended previously for modeling of stratospheric chemistry.

Notes: The reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k1 = 2.1 × 1012 cm3/mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k-1 = 1 × 1010 cm3/mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm Br} + {\rm CH}_3 {\rm CO}\buildrel2\over\rightarrow[{\rm CH}_3 {\rm COBr}]^* \buildrel3\over\rightarrow{\rm HBr} + {\rm CH}_2 {\rm CO}$$\end{document} in which step 2 is shown to be rate limiting under VLPR conditions and k2 is estimated at 1012.6 cm3/mol s from recent theoretical models for radical recombination. It is also shown that 0 ≤ E1 ≤ 1.4 kcal/mol using theoretical models for calculation of A1 and is probably closer to the lower limit. Reaction -1 is negligible under conditions used.

Notes: The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10%. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

Notes: The extinction coefficients and the decay kinetics of I2-. and (SCN)2-⋅ have been characterized over the 15-90°C-temperature range. The extinction coefficients of I2-⋅ at 385 and 725 nm were determined to be 10,000 and 2560M-1 cm-1, respectively, based on the extinction coefficient of (SCN)2-⋅ at 475 nm being equal to 7600M-1 cm-1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I2-⋅ and (SCN)2-⋅ was found to be a function of I- and SCN- concentration, respectively, as well as temperature.

Notes: The pyrolysis kinetics of several ethyl esters with polar substituents at the acyl carbon have been studied in the temperature range of 319.8-400.0°C and pressure range of 50.5-178.0 torr. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for ethyl glycolate, log k1 (s-1) = (12.75 ± 0.30) - (201.4 ± 3.8) kJ/mol/2.303RT; for ethyl cyanoacetate, log k1 (s-1) = (12.19 ± 0.18) - (191.8 ± 2.1) kJ/mol/2.303RT; for ethyl dichloroacetate, log k1 (s-1) = (12.62 ± 0.36) - (193.9 ± 4.3) kJ/mol/2.303RT; for ethyl trichloroacetate, log k1 (s-1) = (12.27 ± 0.09) - (185.1 ± 1.0) kJ/mol/2.303RT. The results of the present work together with those reported recently in the literature give an approximate linear correlation when plotting log k/k0 vs. σ* values (ρ* = 0.315 ± 0.004, r = 0.976, and intercept = 0.032 ± 0.006 at 400°C). This linear relationship indicates that the polar substituents affect the rate of elimination by electronic factors. The greater the electronegative nature of the polar substituent, the faster is the pyrolysis rate. The alkyl substituents yield, within experimental error, similar values in rates which makes difficult an adequate assessment of their real influence.

Notes: Mathematical modeling was used for the kinetics of gas-phase propane oxidation at 586, 613, and 658 K and pressures 172 and 250 torr. The reaction mechanism involving branching by decay of the peracetyl peroxy radical, and oxygen-containing products formed on decay of the RO4 radical is discussed. Fair agreement between calculated and experimental results on the kinetics and accumulation rates of reaction products was obtained.

Notes: The termolecular rate constant for the reaction Cl + NO2 + M has been measured over the temperature range 264 to 417 K and at pressure 1 to 7 torr in a discharge flow system using atomic chlorine resonance fluorescence at 140 nm to monitor the decay of Cl in an excess of NO2. The results are\documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm He}} = 9.4{\rm } \times {\rm }10^{ - 31} \left({\frac{T}{{300}}} \right)^{ - 2.0 \pm 0.05} {\rm cm}^6 {\rm s}^{ - {\rm 1}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm N}2} = (14.8{\rm } \pm {\rm }1.4){\rm } \times {\rm 10}^{ - 31} {\rm cm}^6 {\rm s}^{ - 1}$\end{document} at 296 K where error limits represent one standard deviation. The systematic error of k1 measurements is estimated to be about 15%. Using a static photolysis system coupled with the FTIR spectrophotometer the branching ratio for the formation of the two possible isomers was found to be ClONO(≥75%) and CINO2(≤25%) in good agreement with previous measurements.

Notes: Absolute values of the rate constants for the reaction of hydrogen atoms with cyclic olefins in the gas phase have been measured in a discharge-flow system under 3.5, 16, and 22 torr Ar at 23°C. The attenuation of hydrogen atom concentration in the reaction tube in the presence of a large excess of olefin was measured with an ESR spectrometer, and the products were analyzed by gas chromatography. Cyclic C6 hydrocarbons were the only significant products obtained when the hydrogen atom concentration was 2.6 × 10-10 mole/1., the olefin concentration was in the range of 9 to 22 × 10-8 mole/1., and the pressure was 16 torr Ar. The values for the rate constants for reaction with cyclohexadiene-1,3, cyclohexadiene-1,4, and cyclohexene are, respectively, (9 ± 2) × 108, (12 ± 1) × 108, and (6 ± 1) × 108 l./mole-sec, and they are not changed significantly by a sixfold change in total pressure. The fraction of the total interaction that proceeds by addition is 84% in the cyclohexadiene-1,3 system, but only 18% in the cyclohexadiene-1,4 system, and the cyclohexadienyl radical is therefore the dominant radical species in the latter system. The pattern of interaction between the hydrogen atom and the cyclohexadienyl radical was determined, and comprises 65% of disproportionation, and 13% and 23% of combination to yield cyclohexadiene-1,3 and cyclohexadiene-1,4, respectively. These results are consistent with the general patterns of reactivity emerging from studies of the reactions between free radicals and olefins in related systems.

Notes: Different possible mechanisms for the gas phase reaction of formation of bromine chloride from bromine and chlorine are discussed. The rate of the reaction has been deduced from photometric measurements in conventional static reactors of surface-to-volume ratio ranging between 0.6 and 3 cm-1, at temperatures between 51 and 113°C. Experimental data show that (1) the observed reaction is predominantly heterogeneous, and (2) the homogeneous reaction must proceed by an atomic chain mechanism initiated by Br atoms.

Notes: The kinetics of the reaction between ozone and allene (A) were studied in the range of 226 to 325°K in the gas phase. Initial O3 pressures varied from 0.01 to 0.7 torr and allene pressures varied from 0.05 to 6 torr. At the higher initial O3 pressures the most important product was O2 followed by CO, H2O, CO2, and C2H4. Oxygen balances averaging about 110% were obtained, which implies that no important oxygenated products were missed. However, carbon balances were only about 50% and hydrogen balances were even less, so that unidentified hydrocarbons were presumably formed. The rate law found was - d[O3]/dt = k1[O3][A] + k2a[O3]2[A]/[O3]0 where log k1(M-1sec-1) = 6.0 ± 0.7 - (5500±1000)/2.30RT and log k2a(M-1sec-1) = 6.9 ± 0.7 - (6200 ± 800/2.30RT). A mechanism is proposed which accounts for the rate law and the observed stoichiometry of O2 formed-O3 used. This involves a heterogeneous catalyzed decomposition of O3. The rate constant k1 is identified with the primary addition reaction A + O3 → AO3, and this rate constant is compared with those from other O3 addition reactions.